In recent years, energy conservation of power consumption of electronic equipment is required, and therefore the demand for a power semiconductor capable of converting an electric power with high efficiency increases. The power semiconductor is principally used for home electric appliances such as an air conditioner whose power consumption is high and for power control of a hybrid car, an electric vehicle and the like. Particularly, in-vehicle power semiconductors for hybrid cars and electric vehicles requires a large current capacity and requires a cooling system having a high heat-dissipating property. Heat generated in the power semiconductor is transferred to a heatsink through a heat spreader and cooled, and the heat spreader can be bonded to the heatsink using a highly thermally conductive adhesive agent. Since metal such as copper or aluminum is used for the heat spreader and the heatsink, high adhesive strength to these metals is required of the highly thermally conductive adhesive agent, and furthermore in the in-vehicle power semiconductor application, high bonding reliability such that there is no peeling nor crack in a cooling/heating cycle test, is required from usage environment.
As a material used for the highly thermally conductive adhesive agent, there is proposed a resin composition prepared by adding inorganic fillers having high thermal conductivity to a thermosetting resin such as an epoxy resin, to increase the thermal conductivity of the composition (refer to, for example, Patent Document 1). Also, in the adhesive agent containing a polyimide resin or a polyimide silicone resin, there is proposed an adhesive composition in which thermal conductivity, heat resistance, and adhesiveness are improved by adding inorganic fillers having high thermal conductance (refer to, for example, Patent Document 2). Furthermore, there is proposed a highly thermally conductive resin composition in which bonding reliability is improved while alleviating stress in a cooling/heating cycle by adding inorganic fillers having high thermal conductivity to a highly flexible epoxy resin composed of an aliphatic chain (for example, Patent Document 3).